Persistent impairments in neurocognitive function have been described in bipolar disorder.

To compare the cognitive performance of patients with bipolar II disorder with that of patients with bipolar I disorder and a healthy control group.

The study included 71 euthymic patients with bipolar disorder (38 bipolar I, 33 bipolar II), who were compared on clinical and neuropsychological variables (e.g. executive function, attention, verbal and visual memory) and contrasted with 35 healthy controls on cognitive performance.

Compared with controls, both bipolar groups showed significant deficits in most cognitive tasks including working memory (Digit Span Backwards, P=0.002) and attention (Digit Span Forwards, P=0.005; Trail Making Test, P=0.001). Those with type II disorders had an intermediate level of performance between the bipolar I group and the control group in verbal memory (P < 0.005) and executive functions (Stroop interference task, P=0.020).

Cognitive impairment exists in both subtypes of bipolar disorder, although more so in the bipolar I group. The best predictors of poor psychosocial functioning in bipolar II disorder were subclinical depressive symptoms, early onset of illness and poor performance on a measure related to executive function.